1. Field of Invention
This invention relates to filtration systems which separate solids from liquids in process flows. More specifically, this invention is an improved, low-cost filter bag used to remove solids from industrial process flows.
The invention includes a greater amount of filter media surface area than comparably sized prior art filter bags, provides the additional surface area without a corresponding restriction in flow, includes a means by which the growth of the layer of solids retained within the filter bag is uniform throughout the length of the filter bag, and is capable, without collapsing upon itself, of being cleaned by reversing the direction of the process flow. The invention may be utilized in a variety of chemical and/or industrial process flow applications requiring filtration as long as the filter bag is constructed from the appropriate filter media for each flow.
Generally, filter bags are used in industrial process flows to separate solids from liquids. Being permeable only to particles which are smaller than a pre-determined, specific size, the filter bag retains any solid particles in the process flow which are larger than the specific size. On the other hand, any particles which are the specific size or smaller (usually only liquid particles) permeate through the filter bag and continue in the flow. The micron rating of the filter media from which the filter bag is constructed dictates the particle sizes which will be retained by the filter bag and which will permeate through the bag.
During the life of the filter bag, as more solids accumulate, a layer of solids is formed within the filter bag. As the layer becomes thicker, the layer of solids becomes a substantial restriction to the flow of process through the filter bag, and the filter bag must then be replaced or cleaned (hereinafter referred to as the "critical thickness").
It is axiomatic that an increase in the size or surface area of the filter bag provides a corresponding increase in the quantity of solids retained by the filter bag. In addition, an increase in the surface area of the filter bag also increases the usable life of the filter bag by prolonging the time it takes the filter bag to reach the critical thickness of solids. Thus, it is advantageous to maximize the surface area of the filter bag.
However, several limitations exist in maximizing the amount of surface area of a filter bag. First, in order to be used in most, if not all, of the existing process flow equipment and systems, a filter bag must have a specific shape and certain dimensions. Second, as surface area is added to the filter bag (by way of folds or layers to the filter bag), the additional surface area itself tends to act as a restriction to the flow by providing too many obstructions within the filter bag.
The key then is to maximize the filter media surface area without restricting the flow of process through the filter bag. It would thus be advantageous to construct a filter bag which maximizes the filter media surface area without restricting the flow of process through the filter bag.
Another problem inherent in prior art filter bags is that the layer of solids heretofore described tends to concentrate in only one section of the prior art bags. For instance, in the standard type of tubular shaped filter bag, the process flow enters the bag through the bag's open end and exits the bag through the bag's closed end. The great majority of the process flow exits the bag and is filtered by the bag's closed end. Naturally, the layer of solids builds up primarily at the bag's closed end. Since the layer of solid accumulates and grows primarily at one section of the filter bag, the layer grows quickly and reaches the critical thickness of solids much more rapidly than if the layer of solids builds up uniformly throughout the length of the filter bag. It would thus be advantageous to design a filter bag in which the growth of the layer of solids is uniform throughout the length of the filter bag thereby extending the time for the formation of the critical thickness of solids.
In addition, the majority of prior art filter bags can be cleaned only by removing the bags from the process flow equipment and system. Although this cleaning method is prevalent in the field of art, the method can be improved since it ordinarily requires a shut down of the process flow thereby resulting in time and monetary loss to the operator of the facility. It would thus be advantageous to devise a filter bag (and method) which can be cleaned without the need to remove the filter bag from the process flow equipment and system.
A technique sometimes used to clean filter bags which does not require their removal from the process equipment and system is a "backwash operation." During the backwash operation, the process flow is reversed through the filter bag and the solids retained within the filter bag during normal operation are thereby dislodged. This technique, however, is not widely used since, among other reasons, prior art filter bags constructed of flexible filter media tend to collapse once the backwash operation is in effect. It would thus be advantageous to construct a filter bag made of flexible filter media which may be cleaned by a backwash operation and does not collapse during the backwash operation.
2. Related Art
Filter bags and other such filtration mechanisms have long been known to the prior art. Illustrative of such devices are U.S. Pat. No. 2,278,603 issued to Williams in 1942, U.S. Pat. No. 2,314,640 issued to Winslow et al. in 1943, U.S. Pat. No. 2,539,768 issued to Anderson in 1951, U.S. Pat. No. 2,613,814 issued to Moore in 1952, U.S. Pat. No. 2,946,449 issued to Shaw in 1960, U.S. Pat. No. 4,056,374 issued to Hixenbaugh in 1977, U.S. Pat. No. 4,231,770 issued to Johnson, Jr. in 1980, U.S. Pat. No. 4,280,826 issued to Johnson, Jr. in 1981, U.S. Pat. No. 4,297,115 issued to Johnson, Jr. in 1981, U.S. Pat. No. 4,304,580 issued to Gehl et al. in 1981, and U.S. Pat. No. 4,324,571 issued to Johnson, Jr. in 1982.
U.S. Pat. No. 2,278,603 issued to Williams discloses a filter which is at least partially cylindrical in shape. For the purpose of increasing the filter media surface area, the cylindrically shaped filter includes inwardly projecting folds. The inner edges of the folds define the outline of a cone and the depth of the folds increases progressively upwardly. However, the Williams Patent does not disclose, among others, a means by which the growth of the layer of solids within the filter is uniform throughout its length.
The Hixenbaugh Patent discloses a tubular gas filter bag; however, the Hixenbaugh bag does not include, among others, additional filter media surface area (as compared against similarly sized filter bags) or a means by which the growth of the layer of solids within the filter is uniform throughout its length.
Lastly, the family of Johnson, Jr. Patents all disclose a bag type gas filter with at least one supporting structure located within the bag. The supporting structures permit the bags to be cleaned by reversing flow through the filter media. However, the Johnson, Jr. inventions do not include, among others, additional filter media surface area (as compared against similarly sized filter bags).
Though the above mentioned inventions may be helpful for their stated purpose, they can be improved to provide a filter bag for industrial process flows which includes a greater amount of filter media surface area than comparably sized prior art filter bags, includes the additional surface area without a corresponding restriction in the flow, includes a means by which the growth of the layer of solids retained within the filter bag is uniform throughout the length of the filter bag, and is capable, without collapsing upon itself, of being cleaned by reversing the direction of the process flow.